Chemoprevention of lung cancer by tea

Modulation of Gut Microbial Biomarkers and Metabolites in Cancer Management by Tea Compounds

Cancers are causing millions of deaths and leaving a huge clinical and economic burden. High costs of cancer drugs are limiting their access to the growing number of cancer cases. The development of more affordable alternative therapy could reach more patients. As gut microbiota plays a significant role in the development and treatment of cancer, microbiome-targeted therapy has gained more attention in recent years. Dietary and natural compounds can modulate gut microbiota composition while providing broader and more accessible access to medicine. Tea compounds have been shown to have anti-cancer properties as well as modulate the gut microbiota and their related metabolites. However, there is no comprehensive review that focuses on the gut modulatory effects of tea compounds and their impact on reshaping the metabolic profiles, particularly in cancer models. In this review, the effects of different tea compounds on gut microbiota in cancer settings are discussed. Furthermore, the relationship between these modulated bacteria and their related metabolites, along with the mechanisms of how these changes led to cancer intervention are summarized.

Ethanolic extract Ocimum sanctum Linn. induces an apoptosis in human lung adenocarcinoma (A549) cells

Ocimum sanctum (OS) is tropical herbal plant which is easy to find and widely used as a vegetable food in Indonesia. In last decade, lung adenocarcinoma was in top position as male cancer disease in Indonesia. Recently, emerging data showing the extracts of different species of Ocimum exhibiting the anti-tumor properties. Further studies on lung lewis carcinoma demonstrated pro-apoptosis effects after the treatment with Ocimum extracts. However, the effect of OS of Indonesian origin in human alveolar pulmonary adenocarcinoma A549 cells remain unclear. Therefore, we aimed to investigate effects of ethanolic extract OS (EEOS) in A549 cell culture systems. Cell adhesion and viability assays revealed that EEOS significantly decreased the attachment into extracellular matrix of A549 cells. Morphological examination AO/EB and DAPI staining indicated that EEOS induced the cells shrinkage, DNA fragmentation and condensation of A549 cells. Further, EEOS treatment induced the apoptosis rate followed by up-regulation of reactive oxygen species (ROS), caspase-3 expression and decreased anti-apoptotic protein Bcl-2. This condition also suppressed the expression of SOD2 as well as the GPx. In conclusion, our findings indicate that EEOS suppressed the viability of A549 cells, which may result from the activation of ROS promoting the apoptosis signaling via mitochondrial intrinsic pathway. Taken together, EEOS might be a good therapeutic potential to further understand its properties in the treatment of lung carcinoma.

Effects and mechanisms of tea for the prevention and management of cancers: An updated review

Tea is a traditional and popular beverage worldwide, and the consumption of tea has been demonstrated to possess many health benefits, such as cardiovascular protection, anti-obesity, anti-diabetes, and anticancer. Epidemiological studies have shown that the consumption of tea is inversely associated with the risk of several cancers. In addition, experimental studies have revealed that the anticancer actions of tea are mainly attributed to tea polyphenols, such as epigallocatechin-3-gallate and theaflavins. Both in vitro and in vivo studies have demonstrated that the possible anticancer mechanisms are the inhibition on proliferation, anti-angiogenesis, induction of apoptosis, suppression on metastasis, inhibition on cancer stem cells, and modulation on gut microbiota. Its synergetic anticancer effects with drugs or other compounds could promote anticancer therapies. Furthermore, clinical trials have elucidated that intervention of tea phytochemicals is effective in the prevention of several cancers. This paper is an updated review for the prevention and management of cancers by tea based on the findings from epidemiological, experimental and clinical studies, and special attention is paid on the mechanisms of action.

Antitumoral effect of Ocoxin, a natural compound-containing nutritional supplement, in small cell lung cancer

Lung cancer is the most frequently diagnosed neoplasia and represents the leading cause of cancer-related deaths worldwide. Due to this fact, efforts to improve patient survival through the introduction of novel therapies, as well as preventive actions, are urgently required. Considering this scenario, the antitumoral action of the composite formulation Ocoxin^® oral solution (OOS), that contains several antitumoral compounds including antioxidants, was tested in small cell lung cancer (SCLC) in vitro and in vivo preclinical models. OOS exhibited anti-SCLC action that was both time and dose dependent. In vivo OOS decreased the growth of tumors implanted in mice without showing signs of toxicity. The antitumoral effect was due to inhibition of cell proliferation and increased cell death. Genomic and biochemical analyses indicated that OOS augmented p27 and decreased the functioning of several routes involved in cell proliferation. In addition, OOS caused cell death by activation of caspases. Importantly, OOS favored the action of several standard of care drugs used in the SCLC clinic. Our results suggest that OOS has antitumoral action on SCLC, and could be used to supplement the action of drugs commonly used to treat this type of tumor.

Inhibitory effect of the green tea molecule EGCG against dengue virus infection

Dengue virus (DENV) infection is a major public health problem worldwide; however, specific antiviral drugs against it are not available. Hence, identifying effective antiviral agents for the prevention of DENV infection is important. In this study, we showed that the reportedly highly biologically active green-tea component epigallocatechin gallate (EGCG) inhibited dengue virus infection regardless of infecting serotype, but no or minimal inhibition was observed with other flaviviruses, including Japanese encephalitis virus, yellow fever virus, and Zika virus. EGCG exerted its antiviral effect mainly at the early stage of infection, probably by interacting directly with virions to prevent virus infection. Our results suggest that EGCG specifically targets DENV and might be used as a lead structure to develop an antiviral drug for use against the virus.

The Green Tea Polyphenol(-)-epigallocatechin-3-gallate and its beneficial roles in chronic kidney disease

Chronic kidney disease (CKD), a condition that affects around 10% of the population, has become a significant public health concern. Current therapeutic strategies to slow down the progression of CKD remain limited. Thus, it is urgent to develop new strategies to manage the patients with CKD. Work within the past decade has improved our understanding of the mechanisms contributing to CKD. In particular, oxidative stress as well as inflammation appears to play a pivotal role in CKD progression. ()-Epigallocatechin-3-gallate (EGCG), the major catechin of green tea extract, is known as a powerful antioxidant and reactive oxygen species scavenger. Various studies have shown EGCG has a potential role in chronic kidney disease models. It is suggested that EGCG modulates cellular and molecular mechanisms via inflammation-related NF-кB and Nrf2 signaling pathway, as well as apoptosis-related ER stress pathway and mitochondrial pathway. Therefore, based on these studies, this review attempts to present a recent state of our knowledge and understanding of mechanisms of its role on the process of CKD, with the aim of providing some clues for the future optimization of EGCG in renal diseases.

Risk factors for lung cancer worldwide

Lung cancer is the most frequent malignant neoplasm in most countries, and the main cancer-related cause of mortality worldwide in both sexes combined.The geographic and temporal patterns of lung cancer incidence, as well as lung cancer mortality, on a population level are chiefly determined by tobacco consumption, the main aetiological factor in lung carcinogenesis.Other factors such as genetic susceptibility, poor diet, occupational exposures and air pollution may act independently or in concert with tobacco smoking in shaping the descriptive epidemiology of lung cancer. Moreover, novel approaches in the classification of lung cancer based on molecular techniques have started to bring new insights to its aetiology, in particular among nonsmokers. Despite the success in delineation of tobacco smoking as the major risk factor for lung cancer, this highly preventable disease remains among the most common and most lethal cancers globally.Future preventive efforts and research need to focus on non-cigarette tobacco smoking products, as well as better understanding of risk factors underlying lung carcinogenesis in never-smokers.

Association between green tea/coffee consumption and biliary tract cancer: A population-based cohort study in Japan

Green tea and coffee consumption may decrease the risk of some types of cancers. However, their effects on biliary tract cancer (BTC) have been poorly understood. In this population‐based prospective cohort study in Japan, we investigated the association of green tea (total green tea, Sencha, and Bancha/Genmaicha) and coffee consumption with the risk for BTC and its subtypes, gallbladder cancer, and extrahepatic bile duct cancer. The hazard ratios and 95% confidence intervals were calculated using the Cox proportional hazard model. A total of 89 555 people aged 45–74 years were enrolled between 1995 and 1999 and followed up for 1 138 623 person‐years until 2010, during which 284 cases of BTC were identified. Consumption of >720 mL/day green tea was significantly associated with decreased risk compared with consumption of ≤120 mL/day (hazard ratio = 0.67 [95% confidence interval, 0.46–0.97]), and a non‐significant trend of decreased risk associated with increased consumption was observed (P‐trend = 0.095). In the analysis according to the location of the primary tumor, consuming >120 mL green tea tended to be associated with decreased risk of gallbladder cancer and extrahepatic bile duct cancer. When Sencha and Bancha/Genmaicha were analyzed separately, we observed a non‐significant trend of decreased risk of BTC associated with Sencha but no association with Bancha/Genmaicha. For coffee, there was no clear association with biliary tract, gallbladder, or extrahepatic bile duct cancer. Our findings suggest that high green tea consumption may lower the risk of BTC, and the effect may be attributable to Sencha consumption.

Green tea and anticancer perspectives: updates from last decade

Green tea is the most widely consumed beverage besides water and has attained significant attention owing to health benefits against array of maladies, e.g., obesity, diabetes mellitus, cardiovascular disorders, and cancer insurgence. The major bioactive molecules are epigallocatechin-3-gallate, epicatechin, epicatechin-3-gallate, epigallocatechin, etc. The anticarcinogenic and antimutagenic activities of green tea were highlighted some years ago. Several cohort studies and controlled randomized trials suggested the inverse association of green tea consumption and cancer prevalence. Cell culture and animal studies depicted the mechanisms of green tea to control cancer insurgence, i.e., induction of apoptosis to control cell growth arrest, altered expression of cell-cycle regulatory proteins, activation of killer caspases, and suppression of nuclear factor kappa-B activation. It acts as carcinoma blocker by modulating the signal transduction pathways involved in cell proliferation, transformation, inflammation, and metastasis. However, results generated from some research interventions conducted in different groups like smokers and nonsmokers, etc. contradicted with aforementioned anticancer perspectives. In this review paper, anticancer perspectives of green tea and its components have been described. Recent findings and literature have been surfed and arguments are presented to clarify the ambiguities regarding anticancer perspectives of green tea and its component especially against colon, skin, lung, prostate, and breast cancer. The heading of discussion and future trends is limelight of the manuscript. The compiled manuscript provides new avenues for researchers to be explored in relation to green tea and its bioactive components.

Chemopreventive potential of green tea catechins in hepatocellular carcinoma

Hepatocellular carcinoma (HCC), which is a common malignancy worldwide, usually develops in a cirrhotic liver due to hepatitis virus infection. Metabolic syndrome, which is frequently complicated by obesity and diabetes mellitus, is also a critical risk factor for liver carcinogenesis. Green tea catechins (GTCs) may possess potent anticancer and chemopreventive properties for a number of different malignancies, including liver cancer. Antioxidant and anti-inflammatory activities are key mechanisms through which GTCs prevent the development of neoplasms, and they also exert cancer chemopreventive effects by modulating several signaling transduction and metabolic pathways. Furthermore, GTCs are considered to be useful for the prevention of obesity- and metabolic syndrome-related carcinogenesis by improving metabolic disorders. Several interventional trials in humans have shown that GTCs may ameliorate metabolic abnormalities and prevent the development of precancerous lesions. The purpose of this article is to review the key mechanisms by which GTCs exert chemopreventive effects in liver carcinogenesis, focusing especially on their ability to inhibit receptor tyrosine kinases and improve metabolic abnormalities. We also review the evidence for GTCs acting to prevent metabolic syndrome-associated liver carcinogenesis.

Epigallocatechin-3-gallate protects against cisplatin-induced nephrotoxicity by inhibiting endoplasmic reticulum stress-induced apoptosis

Cisplatin (CP)-induced nephrotoxicity hampers its application in clinic. Green tea, particularly its predominant polyphenolic constituent epigallocatechin-3-gallate (EGCG), possesses anti-inflammatory, antioxidant, and anti-apoptotic properties. The present study was designed to investigate the protective effects of EGCG against CP-induced nephrotoxicity in mice. Male C57/BL6 mice in different groups received single injection of CP (20 mg/kg) and EGCG (100 mg/kg) in various sets and kidney tissues and blood were collected after killing. Then, samples were used for biochemical and immunohistochemical assay. Our results showed EGCG decreased biochemical factors and immunohistochemical damage induced by CP. Besides, expression of phosphorylated-extracellular signal-regulated kinase (p-ERK), glucose-regulated protein 78 (GRP78), caspase-12, and apoptosis of kidney were decreased by EGCG via inhibition of endoplasmic reticulum (ER) stress-induced apoptosis.

Tea consumption and lung cancer risk: a meta-analysis of case-control and cohort studies

OBJECTIVE

Recent epidemiologic studies, especially cohort and case-control studies, have yielded inconsistent findings regarding the association between tea consumption and risk for lung cancer. The aim of this study was to assess a potential relationship between tea consumption and the incidence of lung cancer worldwide.

METHODS

A systematic literature search of PubMed, Web of Science, the Cochrane Library, Google Scholar, the Chinese Biomedical Database, and Wanfang Database was conducted from 1966 to January 2014 by two investigators. All cohort studies and case-control studies that evaluated the association of tea and lung cancer were included. Summary relative risks (RR) and the corresponding 95% confidence intervals (CIs) were calculated using a random-effects model. Quality assessments were performed using the Newcastle-Ottawa Scale. Heterogeneity was assessed using the Q and I(2) tests, and the source of heterogeneity was detected by meta-regression analysis. Publication bias was evaluated with Egger's regression symmetry test. Subgroup analyses and sensitivity analysis were performed.

RESULTS

Thirty-eight lung cancer studies (26 case-control studies and 12 cohort studies) with 59,041 cases and 396,664 controls were included. Overall tea consumption was significantly associated with decreased risk for lung cancer (RR, 0.78; 95% CI, 0.70-0.87). Subgroup analyses showed that tea consumption was associated with reduced risk for lung cancer in women (RR, 0.76; 95% CI, 0.62-0.93), case-control studies (RR 0.72; 95% CI 0.63-0.83), Western studies (RR, 0.85; 95% CI, 0.75-0.97), and studies in China and Japan (RR, 0.74; 95% CI, 0.62-0.88). Both green tea (RR, 0.75; 95% CI, 0.62-0.91) and black tea (RR, 0.82; 95% CI, 0.71-0.94) were significantly associated with reduced lung cancer risk. No significant association was found in men or in cohort studies.

CONCLUSION

Tea consumption may offer some protection against lung cancer.

Does tea prevent cancer? Evidence from laboratory and human intervention studies

Tea (Camellia sinensis) is a widely consumed beverage and has been extensively studied for its cancer-preventive activity. Both the polyphenolic constituents as well as the caffeine in tea have been implicated as potential cancer-preventive compounds; the relative importance seems to depend on the cancer type. Green tea and the green tea catechin have been shown to inhibit tumorigenesis at a number of organ sites and to be effective when administered either during the initiation or postinitiation phases of carcinogenesis. Black tea, although not as well studied as green tea, has also shown cancer-preventive effects in laboratory models. A number of potential mechanisms have been proposed to account for the cancer-preventive effects of tea, including modulation of phase II metabolism, alterations in redox environment, inhibition of growth factor signaling, and others. In addition to the laboratory studies, there is a growing body of human intervention studies suggesting that tea can slow cancer progression and modify biomarkers relevant to carcinogenesis. Although available data are promising, many questions remain with regard to the dose-response relations of tea constituents in various models, the primary mechanisms of action, and the potential for combination chemoprevention strategies that involve tea as well as other dietary or pharmaceutical agents. The present review examines the available data from laboratory animal and human intervention studies on tea and cancer prevention. These data were evaluated, and areas for further research are identified.

Anti-infective properties of epigallocatechin-3-gallate (EGCG), a component of green tea

The consumption of green tea (Camellia sinensis) has been shown to have many physiological and pharmacological health benefits. In the past two decades several studies have reported that epigallocatechin-3-gallate (EGCG), the main constituent of green tea, has anti-infective properties. Antiviral activities of EGCG with different modes of action have been demonstrated on diverse families of viruses, such as Retroviridae, Orthomyxoviridae and Flaviviridae and include important human pathogens like human immunodeficiency virus, influenza A virus and the hepatitis C virus. Furthermore, the molecule interferes with the replication cycle of DNA viruses like hepatitis B virus, herpes simplex virus and adenovirus. Most of these studies demonstrated antiviral properties within physiological concentrations of EGCG in vitro. In contrast, the minimum inhibitory concentrations against bacteria were 10-100-fold higher. Nevertheless, the antibacterial effects of EGCG alone and in combination with different antibiotics have been intensively analysed against a number of bacteria including multidrug-resistant strains such as methicillin-resistant Staphylococcus aureus or Stenotrophomonas maltophilia. Furthermore, the catechin EGCG has antifungal activity against human-pathogenic yeasts like Candida albicans. Although the mechanistic effects of EGCG are not fully understood, there are results indicating that EGCG binds to lipid membranes and affects the folic acid metabolism of bacteria and fungi by inhibiting the cytoplasmic enzyme dihydrofolate reductase. This review summarizes the current knowledge and future perspectives on the antibacterial, antifungal and antiviral effects of the green tea constituent EGCG.

The relationship between the structure and biological actions of green tea catechins

Catechins and their gallate esters are a class of polyphenolic compounds. The catechin subclass known as flavan-3-ols have recently attracted much attention with regards to their beneficial effect on human health. Their biological actions are dependent on the structure of the compounds and vary according to cell type. They are best known as powerful antioxidants; however depending on the doses they also exhibit prooxidant effects. The anti- or prooxidant effects of green tea catechins have been implicated in the modulation of several cellular functions often associated with strong chemoprotective properties. This review summarises the benefit catechins to human health, the main molecular pathways modulated by catechins. The relationship between the structure and activity of the catechins needs to be studied further. In the future, the structure of catechins could be modified so as to synthesise novel compounds with more specific beneficial properties and higher bioavailability.

Bioactivity and bioavailability of ginsenosides are dependent on the glycosidase activities of the A/J mouse intestinal microbiome defined by pyrosequencing

PURPOSE

To investigate the ability of bacteria in the intestinal microbiome to convert naturally occurring primary ginsenosides in red ginseng extract to active secondary ginsenosides.

METHODS

Anti-proliferative ginsenoside activity was tested using mouse lung cancer LM1 cells. Permeabilities were evaluated in Caco-2 cell monolayers. Systemic exposure of secondary ginsenosides was determined in A/J mice. 16S rRNA gene pyrosequencing was used to determine membership and abundance of bacteria in intestinal microbiome.

RESULTS

Secondary ginsenoside C-K exhibited higher anti-proliferative activity and permeability than primary ginsenosides. Significant amounts of secondary ginsenosides (F2 and C-K) were found in blood of A/J mice following oral administration of primary ginsenoside Rb1. Because mammalian cells did not hydrolyze ginsenoside, we determined the ability of bacteria to hydrolyze ginsenosides and found that Rb1 underwent stepwise hydrolysis to Rd, F2, and then C-K. Formation of F2 from Rd was the rate-limiting step in the biotransformation of Rb1 to C-K.

CONCLUSION

Conversion to F2 is the rate-limiting step in bioactivation of primary ginsenosides by A/J mouse intestinal microbiome, whose characterization reveals the presence of certain bacterial families capable of enabling the formation of F2 and C-K in vivo.

Lung cancer chemoprevention: difficulties, promise and potential agents?

INTRODUCTION

In a variety of cancers there is evidence that specific regimens can prevent or significantly delay the development of cancer. Thus, for breast cancer (ER+) use of SERMs or aromatase inhibitors can substantially decrease tumor incidence. For cervical cancer, HPV vaccination will inhibit long term cancer incidence. For colon cancer, the second greatest cancer killer, administration of aspirin and other NSAIDs decreases advanced colon adenomas in Phase II trials and epidemiologic data support their ability to prevent colon cancer. To date prevention trials in the area of lung cancer have shown minimal efficacy.

AREAS COVERED

The paper examines and discusses in greater detail certain promising agents which the authors have tested either preclinically and or in early phase clinical trials. These agents include RXR agonists, EGFr inhibitors, NSAIDs and Triterpenoids. Other agents including glucocorticoids, pioglitazone and iloprost are briefly mentioned. In addition, the paper presents various types of potential Phase II lung cancer prevention trials and describes their strengths and weaknesses. The potential use of various biomarkers as endpoints in trials e.g. histopathology, non-specific biomarkers (e.g., Ki67, cyclin D expression, apoptosis) and molecular biomarkers (e.g. specific phosphorylated proteins, gene expression etc.) is presented. Finally, we examine at least one approach, the use of aerosols, which may diminish the systemic toxicity associated with certain of these agents.

EXPERT OPINION

The manuscript presents: a) a number of promising agents which appear applicable to further Phase II prevention trials; b) approaches to defining potential preventive agents as well; c) approaches which might mitigate the side effects associated with potential agents most specifically the use of aerosols. Finally, we discuss biomarker studies both preclinical and clinical which might help support potential Phase II trials. The particular appeal to the preclinical studies is that they can be followed to a tumor endpoint. We hope that this will give the reader further background and allow one to appreciate the potential and some of the hurdles associated with lung cancer chemoprevention.

Green Tea and Lung Cancer

Background: Green tea is a beverage widely used by lung cancer patients and the public for its purported anticancer properties. The authors conducted a systematic review of green tea for the treatment and prevention of lung cancer. Methodology: Six electronic databases were searched from inception until November 2011 for human interventional and preclinical evidence pertaining to the safety and efficacy of green tea for lung cancer. Results: A total of 84 articles met inclusion criteria: two Phase I trials, three reports of one surrogate study, and 79 preclinical studies. There is a lack of controlled trials investigating green tea for lung cancer. Two Phase I studies showed no objective tumor responses at the maximum tolerated dose, ranging from 3 to 4.2 g/m2 green tea extract (GTE) per day. Four cups of green tea daily decreased DNA damage (8OH-dG) in smokers. Human studies indicate that 800mg of green tea catechins daily does not alter activity of the CYP2D6, CYP1A2, CYP3A4 and CYP2C9 enzymes, however in vitro evidence suggests that green tea may bind to and reduce the effectiveness of bortezomib. Green tea applied topically may improve the healing time of radiation burns. Conclusions: Although some evidence suggests that chemopreventative benefits can be accrued from green tea, there is currently insufficient evidence to support green tea as a treatment or preventative agent for lung cancer. Green tea should not be used by patients on bortezomib therapy. Further research is warranted to explore this natural agent for lung cancer treatment and prevention.

Green tea gets molecular

Green tea and its major polyphenolic flavonoid, epigallocatechin gallate (EGCG), have been credited with cancer chemopreventive activity for many years; the mechanism for this activity, however, has remained obscure. Now, as reported in this issue of the journal (beginning on page 1366), Urusova and colleagues showed direct binding of EGCG to the peptidyl prolyl cis/trans isomerase Pin1, which inhibited Pin1 enzymatic activity. They showed that Pin1 expression is required for EGCG effects on cell growth, c-Jun activation, and transcription regulation mediated by NF-κB and activator protein-1. The data provide a glimpse of the mechanism of action of EGCG and set a new bar for the future study of natural products with chemopreventive activity.

The green tea polyphenol (-)-epigallocatechin-3-gallate ameliorates experimental immune-mediated glomerulonephritis

The unchecked overproduction of reactive oxygen and nitrogen species by inflammatory cells can cause tissue damage, intensify inflammation, promote apoptosis, and accelerate the progression of immune-mediated glomerulonephritis (GN). Here we tested whether the anti-inflammatory and antioxidant properties of the green tea polyphenol (-)-epigallocatechin-3-gallate (EGCG) favorably affect the development of immune-mediated GN. Pretreatment of 129/svJ mice with EGCG from 2 days before to 2 weeks after the induction of GN led to reduced proteinuria and serum creatinine, and marked improvement in renal histology when compared with vehicle-pretreated diseased mice. This pretreatment reduced oxidative stress, and normalized osteopontin, p65/nuclear factor-κB, inducible nitric oxide synthase, nitric oxide metabolites, p-Akt, phosphorylated extracellular signal-regulated kinases 1 and 2, p47phox, and myeloperoxidase, all of which were elevated in vehicle-pretreated diseased mice. Levels of glutathione peroxidase and peroxisome proliferator-activated receptor-γ (PPARγ), both reduced in the vehicle-pretreated diseased mice, were normalized. This renoprotective effect was reversed by concomitant administration of the PPARγ antagonist GW9662 throughout the EGCG pretreatment period. Importantly, mortality and renal dysfunction were significantly attenuated even when the polyphenol treatment was initiated 1 week after the onset of GN. Thus, EGCG reversed the progression of immune-mediated GN in mice by targeting redox and inflammatory pathways.

Green tea and cancer prevention

Extracts of green tea and green tea polyphenols have exhibited inhibitory effects against the formation and development of tumors at different organ sites in animals. These include animal models for skin, lung, oral cavity, esophagus, stomach, intestine, colon, liver, pancreas, bladder, mammary gland, and prostate cancers. In addition to suppressing cell proliferation, promoting apoptosis, and modulating signaling transduction, green tea polyphenols, especially (-)-epigallocatechin-3-gallate, also inhibit cell invasion, angiogenesis, and metastasis. This article reviews data on the cancer preventive activities of green tea polyphenols, possible mechanisms involved, and the relationship between green tea consumption and human cancer risk.

Ocimum gratissimum Aqueous Extract Induces Apoptotic Signalling in Lung Adenocarcinoma Cell A549

Ocimum gratissimum (OG) is widely used as a traditional herb for its antibacterial activity in Taiwan. Recently, antitumor effect of OG on breast cancer cell is also reported; however, the effects of OG on human pulmonary adenocarcinoma cell A549 remain unclear. Therefore, we aimed to investigate whether aqueous OG extract (OGE) affects viability of A549 cells and the signals induced by OGE in A549 cells. Cell viability assays revealed that OGE significantly and dose-dependently decreased the viability of A549 cell but not that of BEAS-2B cell. Morphological examination and DAPI staining indicated that OGE induced cell shrinkage and DNA condensation for A549 cells. Further investigation showed that OGE enhanced activation of caspase-3, caspase-9 and caspase-8 and increased protein level of Apaf-1 and Bak, but diminished the level of Bcl-2. Additionally, OGE inhibited the phosphorylation of extracellular signal-regulated kinase (ERK) yet enhanced the phosphorylation of c-Jun N-terminal kinase (JNK) and p38 MAP kinase (p38). In conclusion, our findings indicate that OGE suppressed the cell viability of A549 cells, which may result from the activation of apoptotic signaling and the inhibition of anti-apoptotic signaling, suggesting that OGE might be beneficial to lung carcinoma treatment.

Candidate dietary phytochemicals modulate expression of phase II enzymes GSTP1 and NQO1 in human lung cells

Many phytochemicals possess cancer-preventive properties, some putatively through phase II metabolism-mediated mutagen/oxidant quenching. We applied human lung cells in vitro to investigate the effects of several candidate phytopreventive agents, including green tea extracts (GTE), broccoli sprout extracts (BSE), epigallocatechin gallate (EGCG), sulforaphane (SFN), phenethyl isothiocyanate (PEITC), and benzyl isothiocyanate (BITC), on inducing phase II enzymes glutathione S-transferase P1 (GSTP1) and NAD(P)H:quinone oxidoreductase 1 (NQO1) at mRNA and protein levels. Primary normal human bronchial epithelial cells (NHBE), immortalized human bronchial epithelial cells (HBEC), and lung adenocarcinoma cells (A549) were exposed to diet-achievable levels of GTE and BSE (0.5, 1.0, 2.0 mg/L), or individual index components EGCG, SFN, PEITC, BITC (0.5, 1.0, 2.0 micromol/L) for 24 h, 48 h, and 6 d, respectively. mRNA assays employed RNA-specific quantitative RT-PCR and protein assays employed Western blotting. We found that in NHBE cells, while GSTP1 mRNA levels were slightly but significantly increased after exposure to GTE or BSE, NQO1 mRNA increased to 2- to 4-fold that of control when exposed to GTE, BSE, or SFN. Effects on NQO1 mRNA expression in HBEC cells were similar. NQO1 protein expression increased up to 11.8-fold in SFN-treated NHBE cells. Both GSTP1 and NQO1 protein expression in A549 cells were constitutively high but not induced under any condition. Our results suggest that NQO1 is more responsive to the studied chemopreventive agents than GSTP1 in human lung cells and there is discordance between single agent and complex mixture effects. We conclude that modulation of lung cell phase II metabolism by chemopreventive agents requires cell- and agent-specific discovery and testing.

Protective activity of Theobroma cacao L. phenolic extract on AML12 and MLP29 liver cells by preventing apoptosis and inducing autophagy

Theobroma cacao L. is known to have potential cardiovascular and cancer chemopreventive activities because of its high content of phenolic phytochemicals and their antioxidant capacities. In this work, we show for the first time that cocoa inhibits drug-triggered liver cytotoxicity by inducing autophagy. Phenolic-rich extracts of both unroasted and roasted cocoa prevented Celecoxib-induced cell viability inhibition in MLP29 liver cells because of the accumulation of G1 cells and cell death. Death prevented by cocoa had hallmarks of apoptosis such as the sub-G1 peak at flow cytometry and activation of Bax expression, together with down-regulation of Bcl-2, released cytochrome c in the cytosol with activation of Caspase 3, indicating that components of the apoptotic pathway such as Bax or upstream are major targets of cocoa phytochemicals. The protective effect of cocoa against liver cytotoxicity by Celecoxib was probably accounted for by inducing the autophagic process, as shown by enhanced Beclin 1 expression and accumulation of monodansylcadaverine in autolysosomes. This fact suggests that apoptosis was prevented by inducing autophagy. Finally, considering all these findings, we suggest that cocoa can be added to the list of natural chemopreventive agents whose potential in hepatopathy prevention and therapy should be evaluated.

Taxane analogues against lung cancer: a quantitative structure-activity relationship study

Lung cancer is the second most common cancer in both men (after prostate cancer) and women (after breast cancer). The microtubule-stabilizing taxane such as docetaxel is the only agent currently approved for both first- and second-line treatment of advanced non-small cell lung cancer. Although docetaxel has made significant progress in the treatment of lung cancers either using alone or in combination with various novel targeted agents, its use often results in various undesired side-effects. These limitations have led to the search for new taxane derivatives with fewer side-effects, superior pharmacological properties, and improved anticancer activity to maximize the induced benefits for lung cancer patients. Herein, four series of taxane derivatives were used to correlate their inhibitory activities against lung cancer cells with hydrophobic and steric descriptors to gain a better understanding of their chemical-biological interactions. A parabolic correlation with MR(Y) is the most encouraging example, in which the optimum value of this parameter is well defined. On the basis of this quantitative structure-activity relationship model, six compounds (3-23 to 3-28) are suggested as potential synthetic targets. Internal (cross-validation (q(2)), quality factor (Q), Fischer statistics (F ) and Y-randomization) and external validation tests have validated all the quantitative structure-activity relationship models.

Chemoprevention of lung carcinogenesis in addicted smokers and ex-smokers

Chemoprevention of lung carcinogenesis is one approach to controlling the epidemic of lung cancer caused by cigarette smoking. The target for chemoprevention should be the activities of the multiple carcinogens, toxicants, co-carcinogens, tumour promoters and inflammatory compounds in cigarette smoke. At present there are many agents, both synthetic and naturally occurring, that prevent lung tumour development in well-established animal models. It seems likely that logically constructed mixtures of these agents, developed from the ground up, will be necessary for the prevention of lung carcinogenesis.

Cancer prevention by tea: animal studies, molecular mechanisms and human relevance

Extracts of tea, especially green tea, and tea polyphenols have been shown to inhibit the formation and development of tumours at different organ sites in animal models. There is considerable evidence that tea polyphenols, in particular (-)-epigallocatechin-3-gallate, inhibit enzyme activities and signal transduction pathways, resulting in the suppression of cell proliferation and enhancement of apoptosis, as well as the inhibition of cell invasion,angiogenesis and metastasis. Here, we review these biological activities and existing data relating tea consumption to human cancer risk in an attempt to understand the potential use of tea for cancer prevention.

Green tea: nature's defense against malignancies

The current practice of introducing phytochemicals to support the immune system or fight against diseases is based on centuries old traditions. Nutritional support is a recent advancement in the domain of diet-based therapies; green tea and its constituents are one of the important components of these strategies to prevent and cure various malignancies. The anti-carcinogenic and anti-mutagenic activities of green tea were highlighted some years ago suggesting that it could reduce the prevalence of cancer and even provide protection. The pharmacological actions of green tea are mainly attributed to polyphenols that includes epigallocatechin-3-gallate (EGCG), epicatechin, epicatechin-3-gallate, epigallocatechin. Green tea and its components effectively mitigate cellular damage arising due to oxidative stress. Green tea is supposed to enhance humoral and cell-mediated immunity, decreasing the risk of certain cancers, and may have certain advantage in treating inflammatory disorders. Much of the cancer chemopreventive properties of green tea are mediated by EGCG that induces apoptosis and promotes cell growth arrest, by altering the expression of cell cycle regulatory proteins, activating killer caspases, and suppressing nuclear factor kappa-B activation. Besides, it regulates and promotes IL-23 dependent DNA repair and stimulates cytotoxic T cells activities in a tumor microenvironment. It also blocks carcinogenesis by modulating the signal transduction pathways involved in cell proliferation, transformation, inflammation and metastasis. The review is intended to highlight the chemistry of green tea, its antioxidant potential, its immunopotentiating properties and mode of action against various cancer cell lines that showed its potential as a chemopreventive agent against colon, skin, lung, prostate, and breast cancer.

Protandim, a fundamentally new antioxidant approach in chemoprevention using mouse two-stage skin carcinogenesis as a model

Oxidative stress is an important contributor to cancer development. Consistent with that, antioxidant enzymes have been demonstrated to suppress tumorigenesis when being elevated both in vitro and in vivo, making induction of these enzymes a more potent approach for cancer prevention. Protandim, a well-defined combination of widely studied medicinal plants, has been shown to induce superoxide dismutase (SOD) and catalase activities and reduce superoxide generation and lipid peroxidation in healthy human subjects. To investigate whether Protandim can suppress tumor formation by a dietary approach, a two-stage mouse skin carcinogenesis study was performed. At the end of the study, the mice on a Protandim-containing basal diet had similar body weight compared with those on the basal diet, which indicated no overt toxicity by Protandim. After three weeks on the diets, there was a significant increase in the expression levels of SOD and catalase, in addition to the increases in SOD activities. Importantly, at the end of the carcinogenesis study, both skin tumor incidence and multiplicity were reduced in the mice on the Protandim diet by 33% and 57% respectively, compared with those on basal diet. Biochemical and histological studies revealed that the Protandim diet suppressed tumor promoter-induced oxidative stress (evidenced by reduction of protein carbonyl levels), cell proliferation (evidenced by reduction of skin hyperplasia and suppression of PKC/JNK/Jun pathway), and inflammation (evidenced by reduction of ICAM-1/VCAM-1 expression, NF-κB binding activity, and nuclear p65/p50 levels). Overall, induction of antioxidant enzymes by Protandim may serve as a practical and potent approach for cancer prevention.

Dietary chemoprevention strategies for induction of phase II xenobiotic-metabolizing enzymes in lung carcinogenesis: A review

Lung cancer is the leading cause of cancer mortality for men and women in the United States and is a growing worldwide problem. Protection against lung cancer is associated with higher dietary intake of fruits and vegetables, according to recent large epidemiologic studies. One strategy for lung cancer chemoprevention focuses on the use of agents to modulate the metabolism and disposition of tobacco, environmental and endogenous carcinogens through upregulation of detoxifying phase II enzymes. We summarize the substantial evidence that suggests that induction of phase II enzymes, particularly the glutathione S-transferases, plays a direct role in chemoprotection against lung carcinogenesis. The engagement of the Keap1-Nrf2 complex regulating the antioxidant response element (ARE) signaling pathway has been identified as a key molecular target of chemopreventive phase II inducers in several systems. Monitoring of phase II enzyme induction has led to identification of novel chemopreventive agents such as the isothiocyanate sulforaphane, and the 1,2-dithiole-3-thiones. However, no agents have yet demonstrated clear benefit in human cell systems, or in clinical trials. Alternative strategies include: (a) using intermediate cancer biomarkers for the endpoint in human trials; (b) high-throughput small molecule discovery approaches for induced expression of human phase II genes; and (c) integrative approaches that consider pharmacogenetics, along with pharmacokinetics and pharmacodynamics in target lung tissue. These approaches may lead to a more effective strategy of tailored chemoprevention efforts using compounds with proven human activity.

Green tea catechins inhibit angiogenesis through suppression of STAT3 activation

Previous studies indicate that green tea extract may inhibit breast cancer progression by blocking angiogenesis, although the molecular mechanisms are not well defined. We demonstrate that administration of Polyphenon E (Poly E), a standardized green tea extract, inhibited MDA-MB231 breast cancer and human dermal microvascular endothelial (HMVEC) cell migration and the expression of vascular endothelial growth factor (VEGF) and matrix metalloproteinase 9 (MMP9). In addition, Poly E inhibited VEGF-induced neovascularization in vivo. We also demonstrate that Poly E blocked signal transducers and activators of transcription (STAT) signaling by suppressing interferon-gamma (IFN-gamma)-induced gene transcription via IFN-gamma-activating sequence (GAS) elements and downstream STAT3 activation by inhibiting STAT1 and STAT3 dimerization in MDA-MB231 cells. Transient expression of constitutively active STAT3 significantly reduced the inhibitory effect of Poly E on cell migration and VEGF and MMP9 expression. Taken together, these observations indicate that green tea extract inhibits angiogenesis partly through the disruption of STAT3-mediated transcription of genes, including VEGF.

Bioavailability of polyphenon E flavan-3-ols in humans with an ileostomy

To investigate the degree of absorption of flavan-3-ols in the small intestine, human subjects with an ileostomy ingested 200 mg of Polyphenon E, a green tea extract, after which ileal fluid and urine, collected over a 24-h period, were analyzed by high-performance liquid chromatography with photodiode array and mass spectrometric detection. The data obtained indicated that although approximately 40% of flavan-3-ol intake is recovered in ileal fluid, substantial quantities are absorbed in the small intestine. Moreover, 14 urinary metabolites, comprising sulfates, glucuronide, and methylated derivatives, were identified and quantified. All were metabolites of (epi)catechin or (epi)gallocatechin, representing 47 +/- 2% and 26 +/- 9%, respectively, of the ingested parent compound. These high recoveries indicate that these flavan-3-ols absorbed in the small intestine are much more bioavailable than most dietary flavonoids. No 3-O-galloylated flavan-3-ols or their metabolites were detected in urine. The absence of urinary flavan-3-ol metabolites after ingestion of 200 mg of (-)-epigallocatechin gallate indicates that there is no removal of the 3-O-galloyl group in vivo, and hence, this does not account for the high urinary recovery of (epi)gallocatechin metabolites after ingestion of Polyphenon E. Increasing the intake of Polyphenon E, by feeding doses of 200, 500, and 1500 mg, led to increased urinary excretion of (epi)catechin metabolites but not metabolites of (epi)gallocatechin. Coingestion of 200 mg of Polyphenon E with bread, cheese, or glucose did not significantly modify the absorption, metabolism, and excretion of flavan-3-ols. It does not necessarily follow, however, that the same would occur when flavan-3-ols are ingested with more complex food matrices.

Chemoprevention of dibenzo[a,l]pyrene transplacental carcinogenesis in mice born to mothers administered green tea: primary role of caffeine

Our laboratory recently developed a mouse model of transplacental induction of lymphoma, lung and liver cancer by the polycyclic aromatic hydrocarbon, dibenzo[a,l]pyrene (DBP). Pregnant B6129SF1 females, bred to 129S1/SvIm males, were treated on day 17 of gestation with an oral dose of 15 mg/kg DBP. Beginning on day 0 of gestation, dams were given (ad lib) buffered water, 0.5% green tea, 0.5% decaffeinated green tea, caffeine or epigallocatechin-3-gallate (EGCG) (both at equivalent concentrations found in tea). The concentration of the teas (and corresponding caffeine and EGCG) was increased to 1.0% upon entering the second trimester, 1.5% at onset of the third trimester and continued at 1.5% until pups were weaned at 21 days of age. Offspring were raised with normal drinking water and AIN93G diet. Beginning at 2 months of age, offspring experienced significant mortalities due to an aggressive T-cell lymphoma as seen in our previous studies. Ingestion of caffeinated, but not decaffeinated, green tea provided modest but significant protection (P = 0.03) against mortality. Caffeine provided a more robust (P = 0.006) protection, but EGCG was without effect. Offspring also developed DBP-dependent lung adenomas. All treatments significantly reduced lung tumor multiplicity relative to controls (P < 0.02). EGCG was most effective at decreasing tumor burden (P = 0.005) by on average over 40% compared with controls. Induction of Cytochrome P450 (Cyp)1b1 in maternal liver may reduce bioavailability of DBP to the fetus as a mechanism of chemoprevention. This is the first demonstration that maternal ingestion of green tea, during pregnancy and nursing, provides protection against transplacental carcinogenesis.

Effect of dietary green tea extract and aerosolized difluoromethylornithine during lung tumor progression in A/J strain mice

Chemoprevention strategies to prevent the development of lung cancer in at-risk individuals are a key component in disease management. In addition to being highly effective, an ideal chemopreventive agent will require low toxicity as patients are likely to require treatment for several years before their risk of cancer is lowered to background levels. In principle, a combination of safe agents that work through distinct mechanisms will improve efficacy while simultaneously maintaining a favorable safety profile. Here, we describe the use of the decaffeinated green tea extract Polyphenon E (Poly E) (1% in diet) and aerosolized difluoromethylornithine (DFMO) (20 mg/kg/day, 5 days/week) in a mouse lung cancer chemoprevention study using a progression protocol. Female A/J mice were injected with benzo[a]pyrene (B[a]P) at 8 weeks of age and precancerous lesions allowed to form over a period of 21 weeks before chemoprevention treatment for an additional 25 weeks. Poly E treatment did not significantly inhibit average tumor multiplicity but reduced per animal tumor load. Analysis of tumor pathology revealed a specific inhibition of carcinomas, with the largest carcinomas significantly decreased in Poly E-treated animals. Aerosolized DFMO did not have a significant effect on lung tumor progression. Magnetic resonance imaging of B[a]P-induced lung tumors confirmed the presence of a subset of large, rapidly growing tumors in untreated mice. Our results suggest a potential role for green tea extracts in preventing the progression of large, aggressive lung adenocarcinomas.

Inhibition of carcinogenesis by tea constituents

The possible cancer preventive activity of tea has received much attention in recent years. The inhibitory activities of tea and tea constituents against carcinogenesis at different organ sites have been demonstrated in many animal models. The effect of tea consumption on human cancers, however, remains inconclusive. The mechanisms of action of tea polyphenols, especially EGCG, the most abundant and active catechin, have been extensively investigated. Most of the studies, however, were based on cell culture systems, and these mechanisms need to be evaluated and verified in animal models or humans in order to gain more understanding on the effect of tea consumption on human cancer. Human intervention trials are warranted to determine the possible prevention of cancer of specific sites by preparation of tea constituents.

The green tea polyphenol, epigallocatechin-3-gallate inhibits telomerase and induces apoptosis in drug-resistant lung cancer cells

Epidemiological studies on humans and investigations in animal models suggest that consumption of green tea has anti-cancer effects. Small-cell lung carcinoma (SCLC) has a poor prognosis, particularly due to the development of drug resistance. We investigated the effects of the green tea polyphenol, epigallocatechin-3-gallate (EGCG) on human SCLC cells. EGCG had similar effects (IC(50) of approximately 70 microM) on drug-sensitive (H69) and drug-resistant (H69VP) SCLC cells, indicating that it is not part of the drug resistance phenotype expressed in these cells. In both cell lines, incubation in EGCG at 1 x IC(50) for 24h resulted in 50-60% reduced telomerase activity as measured by a PCR-based assay for telomeric repeats. Colorimetric assays of cells treated for 36 h with EGCG demonstrated a reduction in activities of caspases 3 (50%) and 9 (70%) but not caspase 8, indicating initiation of apoptosis. DNA fragmentation as measured by ELISA occurred within cells treated with EGCG and this was confirmed by TUNEL staining. Flow cytometric analysis of SCLC cells incubated for 36 h in EGCG indicated a cell-cycle block in S phase. These data indicate the potential use of EGCG, and possibly green tea, in treating SCLC.

Inhibition of mammary tumorigenesis in the C3(1)/SV40 mouse model by green tea

Previous studies show inhibitory effects of green tea in chemically induced mammary tumors or human tumor explants, but not in spontaneous tumor models that are more representative of human breast cancer. The C3(1)/SV40 mouse model is particularly suited for breast cancer prevention studies because it produces spontaneous ductal adenocarcinomas and a predictable time course for mammary tumorigenesis through a multistage progression similar to that occurring in humans. We therefore used this model to test the chemoprotective effects of green tea. Administration of 0.5% Polyphenon E (Poly E) (a standardized preparation of green tea extract) in drinking water delayed tumor onset and suppressed tumor growth by 40%, compared to tap water-fed animals, with no adverse side effects. Histological analysis of mammary glands showed that green tea slowed the progression of ductal lesions to advanced mammary intraepithelial neoplasias and suppressed tumor invasiveness. Green tea inhibited the proliferation of ductal epithelial cells and tumors and, overall, disrupted post-pubertal ductal growth. Immunohistochemical analyses also demonstrated that green tea inhibited angiogenesis through a decrease in both ductal epithelial and stromal VEGF expression and a decrease in intratumoral microvascular density. Our data strongly support the potential use of green tea as a breast cancer chemopreventive agent.

Structure-activity relationships of tea compounds against human cancer cells

The content of the biologically active amino acid theanine in 15 commercial black, green, specialty, and herbal tea leaves was determined as the 2,4-dinitrophenyltheanine derivative (DNP-theanine) by a validated HPLC method. To define relative anticarcinogenic potencies of tea compounds and teas, nine green tea catechins, three black tea theaflavins, and theanine as well as aqueous and 80% ethanol/water extracts of the same tea leaves were evaluated for their ability to induce cell death in human cancer and normal cells using a tetrazolium microculture (MTT) assay. Compared to untreated controls, most catechins, theaflavins, theanine, and all tea extracts reduced the numbers of the following human cancer cell lines: breast (MCF-7), colon (HT-29), hepatoma (liver) (HepG2), and prostate (PC-3) as well as normal human liver cells (Chang). The growth of normal human lung (HEL299) cells was not inhibited. The destruction of cancer cells was also observed visually by reverse phase microscopy. Statistical analysis of the data showed that (a) the anticarcinogenic effects of tea compounds and of tea leaf extracts varied widely and were concentration dependent over the ranges from 50 to 400 microg/mL of tea compound and from 50 to 400 microg/g of tea solids; (b) the different cancer cells varied in their susceptibilities to destruction; (c) 80% ethanol/water extracts with higher levels of flavonoids determined by HPLC were in most cases more active than the corresponding water extracts; and (d) flavonoid levels of the teas did not directly correlate with anticarcinogenic activities. The findings extend related observations on the anticarcinogenic potential of tea ingredients and suggest that consumers may benefit more by drinking both green and black teas.

Inhibition of adenoma progression to adenocarcinoma in a 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone-induced lung tumorigenesis model in A/J mice by tea polyphenols and caffeine

The present study investigated the inhibitory effects of Polyphenon E [a standardized green tea polyphenol preparation containing 65% (-)-epigallocatechin-3-gallate] and caffeine on 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)-induced lung tumor progression from adenoma to adenocarcinoma. Female A/J mice were treated with a single dose of NNK (103 mg/kg body weight, i.p.) and kept for 20 weeks for the mice to develop lung adenomas. The mice were then given a solution of 0.5% Polyphenon E or 0.044% caffeine as the sole source of drinking fluid until week 52. Both treatments significantly decreased the number of visible lung tumors. Histopathologic analysis indicated that Polyphenon E administration significantly reduced the incidence (by 52%) and multiplicity (by 63%) of lung adenocarcinoma. Caffeine also showed marginal inhibitory effects in incidence and multiplicity of adenocarcinoma (by 48% and 49%, respectively). Markers of cell proliferation, apoptosis, and related cell signaling were studied by immunohistochemistry, and the labeling index and staining intensity were quantified by the Image-Pro system. Polyphenon E and caffeine treatment inhibited cell proliferation (by 57% and 50%, respectively) in adenocarcinomas, enhanced apoptosis in adenocarcinomas (by 2.6- and 4-fold, respectively) and adenomas (both by 2.5-fold), and lowered levels of c-Jun and extracellular signal-regulated kinase (Erk) 1/2 phosphorylation. In the normal lung tissues, neither agent had a significant effect on cell proliferation or apoptosis. The results show that tea polyphenols (and perhaps caffeine) inhibit the progression of NNK-induced lung adenoma to adenocarcinoma. This effect is closely associated with decreased cell proliferation, enhanced apoptosis, and lowered levels of c-Jun and Erk1/2 phosphorylation.

Tea and cancer prevention: molecular mechanisms and human relevance

Tea made from the leaves of the plant Camellia sinensis is a popular beverage. The possible cancer-preventive activity of tea and tea polyphenols has been studied extensively. This article briefly reviews studies in animal models, cell lines, and possible relevance of these studies to the prevention of human cancer. The cancer-preventive activity of tea constituents have been demonstrated in many animal models including cancer of the skin, lung, oral cavity, esophagus, stomach, liver, pancreas, small intestine, colon, bladder, prostate, and mammary gland. The major active constituents are polyphenols, of which (-)-epigallocatechin-3-gallate (EGCG) is most abundant, most active, and most studied, and caffeine. The molecular mechanisms of the cancer-preventive action, however, are just beginning to be understood. Studies in cell lines led to the proposal of many mechanisms on the action of EGCG. However, mechanisms based on studies with very high concentrations of EGCG may not be relevant to cancer prevention in vivo. The autooxidation of EGCG in cell culture may also produce activities that do not occur in many internal organs. In contrast to the cancer prevention activity demonstrated in different animal models, no such conclusion can be convincingly drawn from epidemiological studies on tea consumption and human cancers. Even though the human data are inconclusive, tea constituents may still be used for the prevention of cancer at selected organ sites if sufficient concentrations of the agent can be delivered to these organs. Some interesting examples in this area are discussed.